Elizabeth C. Wilkinson

Reversible cleavage and formation of the dioxygen O-O bond within a dicopper complex

A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M2(μ-O)2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M2(O2), and isomers having M2(μ-O)2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu2(μ-η2:η2-O2)]2+ and [Cu2(μ-O)2]2+ cores through kinetic, spectroscopic, and crystallographic studies.

Functional models for iron-bleomycin

Abstract A new pentadentate ligand, N,N -bis(2-pyridylmethyl)- N -bis(2-pyridyl)methylamine (N4Py), has been prepared. The corresponding iron(II) complex, [N4PyFe(CH 3 CN)](ClO 4 ) 2 , serves as a functional model for the active site of iron-bleomycin. Upon treatment with H 2 O 2 the formation of a purple intermediate has been observed, which has been characterized as an iron(III)-hydroperoxide complex. This N4Py-iron-hydroperoxide system has proven to be an active oxidation catalyst.

A nonheme iron(II) complex that models the redox cycle of lipoxygenase

Abstract. The air-stable complex [Fe(6-Me3-TPA)(O2CAr)]+ [1; 6-Me3-TPA=tris(6-methyl-2-pyridylmethyl)amine] has been synthesized as a model for the iron(II) site of lipoxygenase. This iron(II) complex reacts with 0.5 equiv ROOH to form a yellow species, which has been formulated as [FeIII(OH)(6-Me3-TPA)(O2CAr)]+ (2) by electrospray mass spectrometry. Addition of more ROOH converts 2 into a purple species, which is characterized by electrospray ionization mass spectrometry and resonance Raman spectroscopy as [FeIII(OOR)(6-Me3-TPA)(O2CAr)]+. The purple species is metastable and decomposes via Fe-O bond homolysis to regenerate the starting iron(II) complex. These metal-centered transformations parallel the changes observed for lipoxygenase in its reaction with its product hydroperoxide.

Fe(TPA)-catalyzed alkane hydroxylation can be a metal-based oxidation

Abstract The hydroxylation of cyclohexane by t-butyl hydroperoxide using [Fe2O(TPA)2(H2O)2]4+ (1, TPA = tris(2-pyridylmethyl)amine) as the catalyst has been investigated with the use of a syringe pump to control the concentration of the alkyl hydroperoxide. Unlike an alkoxy radical-based radical chain autoxidation mechanism, the reaction observed produces only alcohol (no ketone) with a deuterium kinetic isotope effect of 10, similar to heme-catalyzed hydroxylations. An alkylperoxoiron(III) intermediate can be trapped at −40°C and characterized by a number of spectroscopic methods. A mechanistic scheme is proposed involving this intermediate which either serves as the precursor to the metal-based oxidant or oxidizes the substrate directly.